Monitoring Haskell

What The Haskell Trace SDK Is And What It Is Not
Installation
Usage

Instana's support for monitoring and tracing of Haskell applications is documented in depth on the Instana Haskell Trace SDK's Github page. Its API documentation is available on Hackage.

What The Haskell Trace SDK Is And What It Is Not

The Instana Haskell Trace SDK does not support automatic instrumentation/tracing in the way we support it in most other languages. Instead, the SDK enables you to create spans manually, much like the Instana Trace SDK for Java does. Besides offering a convenient API to create spans, the Haskell Trace SDK also takes care of establishing a connection to the Instana Agent and sending spans to the agent in an efficient way, that does not impede the performance of your production code. Last but not least, it collects runtime metrics and reports them to Instana.

Installation

To use the Instana Haskell Trace SDK in your application, add instana-haskell-trace-sdk to your dependencies (for example to the build-depends section of your cabal file). If you are using stack you might need to add the SDK (with the version number you want to use) to the extra-deps section in your stack.yaml file:

extra-deps:
- instana-haskell-trace-sdk-0.1.0.0

Usage

Initialization

Before using the SDK, you need to initialize it once, usually during application startup.

import qualified Instana.SDK.SDK as InstanaSDK

main :: IO ()
main = do
  -- ... initialize things ...

  -- initialize Instana
  instana <- InstanaSDK.initInstana

  -- ... initialize more things

The value instana :: Instana.SDK.InstanaContext that is returned by InstanaSDK.initInstana is required for all further calls, that is, for creating spans that will be send to the agent. The SDK will try to connect to an agent (asynchronous, in a a separate thread) as soon as it receives the initInstana call.

The SDK can be configured via environment variables or directly in the code by passing configuration parameters to the initialization function, or both.

There are also bracket-style variants of the initialization function, called withInstana and withConfiguredInstana:

Creating Spans

Bracket Style (High Level API)

All functions starting with with accept (among other parameters) an IO action. The SDK will start a span before, then execute the given IO action and complete the span afterwards. Using this style is recommended over the low level API that requires you to start and complete spans yourself.

withRootEntry: Creates an entry span that is the root of a trace (it has no parent span).
withEntry: Creates an entry span that has a parent span.
withHttpEntry: A convenience function that examines an HTTP request for Instana tracing headers and creates an entry span.
withExit: Creates an exit span. This can only be called inside a withRootEntry or an withEntry call, as an exit span needs an entry span as its parent.
withHttpExit: Creates an exit span for a given HTTP client request.

Low Level API/Explicit Start And Complete

startRootEntry: Starts an entry span that is the beginning of a trace (has no parent span). You will need to call completeEntry at some point.
startEntry: Starts an entry span. You will need to call completeEntry at some point.
startHttpEntry: Starts an entry span for an incoming HTTP request.
startExit: Starts an exit span. You need to call completeExit/completeExitWithData at some point with the partial exit span value that is returned by this function.
startHttpExit: Starts an exit span for an outgoing HTTP request.
completeEntry: Finalizes an entry span. This will put the span into the SDK's span buffer for transmission to the Instana agent.
completeExit: Finalizes an exit span. This will put the span into the SDK's span buffer for transmission to the Instana agent.